HP-UX SNAplus2 R7 General Information

SNA Networking
Components of a Subarea Network
1 SNA Networking
SNAplus2 provides Systems Network Architecture (SNA) networking support for HP-UX workstations. SNA is a
set of protocols devised by IBM to facilitate communications between computers.
Over the years, SNA has evolved considerably. Initially, SNA was heavily oriented towards accessing host computers,
and relied on the host to control the entire network. Each network or sub-network was controlled by the host; other
computers communicated directly with the host but not with each other. This old-style SNA is called “subarea
SNA”, and is still widely used.
Today, SNA provides powerful and flexible networking capabilities, enabling direct peer-to-peer communications
between computers in the network (without requiring the intervention of the host). In a full-fledged peer-level
network, elements in the network can communicate as required; but no single computer is in control of the network.
This new-style SNA is called “APPN” (Advanced Peer-to-Peer Networking).
Many SNA networks have elements of both subarea and peer-to-peer networking. As networks migrate from subarea
SNA to APPN, an APPN-capable host can control older systems while acting as a peer to newer systems. Similarly,
a single computer can access both peer computers (in an APPN network) and a host computer (in a subarea network).
Communication with the host is controlled by the host; communication with other computers is peer-to-peer and
does not involve the host.
1.1 Components of a Subarea Network
A simple subarea network includes the following components.
Node
A node is a component or a computer that participates in an SNA network. SNA defines different node types
for different roles in the network.
Host
A host is a mainframe computer compatible with the original IBM System/370. A host is a type 5 node.
Front-End Processor (FEP)
An FEP (also known as a “communication controller”) is a separate processor attached to the host, to manage
the host’s communications with other computers. An FEP is a type 4 node.
Communications Link
Users are often on a separate site from the host, so the two sites need to be connected by a communications
link.
Terminal controller
At the remote end of the communications link is a terminal controller, which controls the use of the link and
routes data to the terminals. The best-known IBM terminal controllers are the 3174 and 3274, but a computer
running SNAplus2 can act as a terminal controller. A terminal controller is a type 2.1 node.
Terminals
Users work at terminals to submit work to the host or run host applications. The best-known IBM terminal
is the 3270.
Printers
Printers such as the IBM 3287 can also be attached to the terminal controller. They can receive output from
the host.
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